The subject of this present invention is a two-wheeled vehicle with rear suspension. It finds its particular application in the field of bicycles with rear suspension, and more particularly of “mountain bikes” with rear suspension.
Conventionally, a mountain bike can have two suspensions, namely a front suspension and a rear suspension. The front suspension can consist of a telescopic fork. For its part, the rear suspension includes an oscillating assembly and a shock-absorber system. The oscillating assembly, which supports the rear wheel, is connected to the front mountain bike chassis by one or more pivoting links. The function of the shock-absorber system is to act as the elastic suspension of the mountain bike chassis, supporting the user while also absorbing the shocks that result from the bouncing of the rear wheel. The function of the pivoting link or links is to guide the bouncing motion of the rear wheel caused by the irregularities of the terrain.
In a first type of rear suspension, the bottom bracket wheel forms an integral part of the oscillating assembly, so that the suspension has no direct influence on the transmission. In fact, regardless of the bouncing of the rear wheel, the distance between the bottom bracket wheel and the axis of the wheel remains constant.
In a second type of rear suspension, the bottom bracket wheel forms an integral part of the chassis, so that the suspension influences the transmission. In fact, as the rear wheel bounces, a variation is observed in the distance between the bottom bracket wheel and the axis of the rear wheel.
This interaction between the suspension and the transmission can provoke what is usually referred to as the pumping effect, which takes the form of an unwanted movement of the chassis, which sinks and rises under the effect of vigorous pedalling.
More precisely, the variation in the chain length as the rear wheel bounces can affect the transmission. In fact, the tension of the chain can influence the suspension and induce the aforementioned pumping effect.
One is already familiar, in particular from document FR 2 827 831, with two-wheeled vehicles with rear suspension, and with two pivoting links, in which the bottom bracket wheel forms an integral part of the front chassis. The rear suspension is composed of a first short rigid bar constituting the first pivoting link, and of a second short rigid bar or a circular eccentric part constituting the second pivoting link, as well as a shock-absorber system. The two pivoting links each connect the oscillating assembly supporting the rear wheel to the front chassis.
With mountain bikes that are equipped with such suspension systems, the top pivot point of the first pivoting link connects the latter to the rear oscillating assembly, and its bottom pivot point connects it to the front chassis.
The problem that then arises is that the suspension system is effective against the pumping effect only for part of the movement of the rear wheel.
In fact, the movement of the virtual pivot point, which is also known as the instantaneous centre of rotation, defined as the intersection of the straight line passing through the two pivot points of the first pivoting link and the straight line passing through the two pivot points of the second pivoting link, is offset from the chain line, from the front to the rear.
Now if this instantaneous centre of rotation is offset upward from the chain line, the transmission tends to harden the suspension by compressing it, and therefore induces the pumping effect.
These systems therefore do not allow the instantaneous centre of rotation to be kept within a space that is sufficiently close to the chain line, and therefore do not adequately limit the pumping effect, throughout the full movement of the rear wheel and during compression or decompression of the shock-absorber system.
The purpose of the invention is therefore to provide a solution to the aforementioned problem, amongst others.
According to a first aspect, the invention therefore relates to a two-wheeled vehicle, in particular a bicycle or a mountain bike, equipped with rear suspension.
The rear suspension includes a front chassis supporting a bottom bracket wheel, and a rear oscillating assembly supporting a rear drive wheel. The rear oscillating assembly is attached to the front chassis by a shock-absorber system, by a top pivoting link having a top pivot point and a bottom pivot point, and by a bottom pivoting link having a rear pivot point and front pivot point.
Characteristically, the top pivot point connects the top pivoting link to the front chassis, the bottom pivot point connects this top pivoting link to the rear oscillating assembly, the rear pivot point connects the bottom pivoting link to the front chassis, and the front pivot point connects the bottom pivoting link to the rear oscillating assembly, so that, during the compression of the shock-absorber system, the top pivoting link oscillates in relation to the chassis, about an axis that is more-or-less perpendicular to the chain line, and the trajectory of the point of intersection between the straight line passing through the two top and bottom pivot points and the straight line passing through the two front and rear pivot points moves from the rear toward the front of the vehicle within a band that is more-or-less parallel to and at a minimum distance from the chain line.
Implementation variants are presented below, and these can be considered alone or in combination.
The straight line passing through the two rear and front pivot points is more-or-less parallel to the chain line.
The bottom pivoting link takes the form of a circular eccentric part in the form of a canister supporting an eccentric axle on either side of the latter, or by a connecting rod.
The rear pivot point is located between two straight lines that are more-or-less parallel to the chain line, and respectively tangential to the smallest and largest chain sprocket wheels.
The intersection point between the straight line passing through the two top and bottom pivot points and the straight line passing through the two front and rear pivot points, remains behind the axis of the bottom bracket wheel during the first 30%, and preferably the first 25% of the compression of the shock-absorber system.
The top pivoting link takes the form of a connecting rod.
The top pivot point is located close to the rear end of the top tube forming the top front part of the front chassis.
The bottom pivot point is located at or close to the junction between the strut forming the top rear part of the rear oscillating assembly, and the bracing tube forming the top front part of this rear oscillating assembly.
The rear pivot point is located close to the bottom end either of the saddle tube forming the front chassis or of the diagonal tube forming the bottom front part of the front chassis.
The front pivot point is located close to or at the junction between the bracing tube forming the front part of the rear oscillating assembly and the base tube forming the bottom rear part of this rear oscillating assembly.
The invention therefore advantageously allows the instantaneous centre of rotation to be kept at a minimum distance from the chain line, thus limiting the pumping phenomenon throughout the full movement of the rear wheel during compression or decompression of the shock-absorber system.